Novel radiation curable compositions

ABSTRACT

A radiation curable composition comprising a novel photoreactive polymer is disclosed comprising a dendritic polymer core with at least one initiating functional group and at least one co-initiating functional group. Suitable radiation curable compositions are varnishes, lacquers,printing inks and radiation curable ink-jet inks. The dendritic polymeric core is preferably a hyperbranched polymer.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of European Application No. 04106772filed Dec. 21, 2004, which is incorporated by reference. In addition,this application claims the benefit of European Application No. 04103389filed Jul. 15, 2004, which is also incorporated by reference; Inaddition, this application claims the benefit of U.S. ProvisionalApplication No. 60/ 602,445 filed Aug. 17, 2004, which is alsoincorporated by reference.

1. Technical Field

The present invention relates to radiation curable compositions with anew type of photoreactive polymer. The photoreactive polymers are usefulin radiation curable compositions such as varnishes, lacquers andprinting inks and especially useful in radiation curable ink-jet inks.

2. Background Art

The vast majority of commercial radiation curable compositions containlow molecular weight photo-initiators and co-initiators. When lowmolecular weight products are not built into the polymer network, theyare prone to diffuse out of the cured composition and can readily beextracted. When radiation curable compositions are used for foodpackaging or dental applications, the amount of extractable residues isa critical issue and needs to be minimized.

Especially Norrish type II initiators are a point of concern regardingextractable residues. Norrish type II photo-initiators always require aco-initiator. A co-initiator or synergist is basically a moleculecapable of transferring a hydrogen atom to the excited state of theNorrish type II initiator. Aliphatic tertiary amines, aromatic aminesand thiols are preferred examples of co-initiators. After transfer of ahydrogen atom to the Norrish type II initiator, the radical generated onthe synergist initiates the polymerization. Theoretically theco-initiator is built into the polymer network. However, it is highlyunlikely that both the hydrogen transfer and the initiation reactionyields are a hundred percent. Side reactions are likely to occur leavingunreacted synergist and side products in the composition. In foodpackaging printed upon with such a radiation curable composition, theselow molecular weight residues remain mobile and if toxic will causehealth risks upon being extracted into the food.

One approach in solving these problems is to design co-initiators andNorrish type II initiators with a higher molecular weight.

JP 2000086713 (TOYO INK) discloses the use of the reaction product of anunsaturated monomer bearing (meth)acryloyl groups or vinyl ether groupshaving an number average molecular weight of more than 500 with aprimary or secondary amine as co-initiator in radiation curablecompositions. However, using this approach only co-initiators with lowfunctionality can be obtained.

EP 434098 A (UNION CARBIDE) discloses the use of amino terminatedpolyoxyalkylenes as co-initiators in radiation curable compositions. Theclaimed polyoxyalkylenes also have a low functionality, requiring theuse of large amounts of unreactive polymer in the matrix compared to lowmolecular weight co-initiators.

WO 0222700 (PERSTORP SPECIALTY CHEM) discloses a radiation curabledendritic oligomer or polymer, characterised in that the radiationcurable dendritic oligomer or polymer normally has at least one terminalgroup of Formula (A):

and normally at least one terminal group of Formula (B)

wherein R1 and R2 individually are hydrogen or methyl and wherein R3 andR4 individually are alkyl, aryl, alkylaryl, arylalkyl, alkylalkoxy,arylalkoxy, said alkyl and/or said aryl optionally having one or morehydroxyl groups. The dendritic polymers are claimed to be of particularinterest for curing under air compared to conventional curable dendriticoligomers. However, these oligomeric co-initiators tend to lose theireffectiveness when coupled to a polymer, which does not containacrylates, as stated in DAVIDSON, Stephen R. Exploring the ScienceTechnology and Applications of UV and EB-curing. LONDON, UK: SITATechnology Ltd, 1999. p. 141. and DAVIDSON, Stephen R., et al. Type IIpolymeric photoinitiators (polyetherimides) with built-in aminesynergist. Journal of Photochemistry and Photobiology, A: Chemistry.1995, vol. 91, no. 2, p. 153-163.

Polymeric initiators have been disclosed in CRIVELLO, J. V., et al.Photoinitiators for Free Radical Cationic and AnionicPhotopolymerisation. Surface Coatings Technology. 1998, vol. III, p.208-224. and CORRALES, T., et al. Free radical macrophotoinitiators: anoverview on recent advances. Journal of Photochemistry and PhotobiologyA: Chemistry. 2003, vol. 159, no. 2, p. 103-114. All the disclosedpolymeric initiators have a conventional linear molecular geometry. Thesolution viscosity of a radiation curable composition is influencedsignificantly using these polymeric initiators.

WO 03033452 (COATES BROTHERS PLC) discloses multifunctional benzophenoneinitiators having the following general structure:

where n is a number from 1 to 6; R3 is hydrogen, methyl or ethyl; Arepresents a group of formula —[O(CHR²CHR¹)_(a)]_(y)—,—[O(CH₂)_(b)CO]_(y), or —[O(CH₂CO]_((y-1))—[O(CHR²CHR¹)_(a)]— (where oneof R¹ and R² is hydrogen and the other is hydrogen, methyl or ethyl); ais from 1 to 2; b is from 4 to 5; y is from 3 to 10; Q is a residue of apolyhydroxy compound having 2 to 6 hydroxyl groups; and x is greaterthan 1 but no greater than the number of available hydroxyl groups in Q.

WO 03033492 (COATES BROTHERS PLC) discloses similar polymeric initiatorshaving the following structure:

where n is a number from 1 to 6; R3 is hydrogen, methyl or ethyl; Arepresents a group of formula —[O(CHR²CHR¹)_(a)]_(y)—,—[O(CH₂)_(b)CO]_(y), or —[O(CH₂CO]_((y-1))—[O(CHR²CHR¹)_(a)]— (where oneof R¹ and R² is hydrogen and the other is hydrogen, methyl or ethyl); ais from 1 to 2; b is from 4 to 5; y is from 3 to 10; Q is a residue of apolyhydroxy compound having 2 to 6 hydroxyl groups; and x is greaterthan 1 but no greater than the number of available hydroxyl groups in Q.

Both WO 03033452 (COATES BROTHERS PLC) and WO 03033492 (COATES BROTHERSPLC) teach that the molecular weight of the multifunctional initiatorsis most preferably lower than 800, since higher molecular weights causean unwanted increase in the viscosity of the radiation curableformulation. This limits the functionality of the multifunctionalinitiator and limits the possibilities to optimize physical properties,such as the compatibility with different radiation curable compositions,to the choice of Q. Using part of the hydroxyl groups of the core tointroduce moieties for optimization of physical properties would lead tomultifunctional initiators with a low functionality. High concentrationsof photoinitiators would then be needed to obtain the required curingsensitivity, thus limiting the possibilities for the composition andhaving a large influence on the properties of the composition and thefinal result.

WO 9717378 (COATES BROTHERS PLC) discloses a different type ofmultifunctional initiators obtained by the reaction of a multifunctionalcore material containing two or more reactive groups and aphotoinitiator or derivative thereof. The photoinitiator or derivativethereof has a reactive group capable of reacting with the reactivegroups of the multifunctional core. The photoinitiators disclosed in WO9717378 (COATES BROTHERS PLC) are low molecular weight compounds, havinga maximum functionality of 6. Depending on the functionality of thepolyfunctional initiator, the molecular weight of the core is preferablyless than 500 for a difunctional initiator, preferable less than 1000for a tetrafunctional initiator and less than 1500 for a hexafunctionalinitiator. For ink-jet applications, a further increase of molecularweight would lead to an unacceptable viscosity of the radiation curableink-jet ink.

WO 9749664 (LAMBSON FINE CHEMICALS) discloses a photoinitiator,comprising a photoreactive portion and a pendant group, thephotoreactive portion including an aromatic moiety and the pending groupincorporating at least one optionally substituted poly(alkylene glycol)moiety. Preferred photoreactive portions include optionally substitutedbenzophenone, thioxanthone and anthraquinone compounds substituted by apolyethylene glycol or polypropylene glycol moiety of an averagemolecular weight in the range 150 to 900. These types of initiators areessentially monofunctional. The molecular weight per photoreactivemoiety is high. For an equal molar initiator concentration, a highweight percentage of these macromolecular initiators are requiredcompared to their low molecular weight counterparts. As a result a highamount of unreactive polymer is introduced in the radiation curableformulation, having a negative influence on physical properties such asscratch resistance.

Especially in ink-jet applications, a significant increase in thesolution viscosity has to be avoided to keep the ink-jet ink jettable.One approach to reduce problems of high viscosity and low functionalitycaused by these polymeric initiators and co-initiators is to combine theinitiator and co-initiator in the same macromolecule.

Some combinations of a co-initiator and an initiator in a polymer havebeen described. Poly(ethylene imines) derivatized with thioxanthonemoieties have been reported by Jiang et al. (Polymer, 45 (2004),133-140).

In another approach, Jiang and Yin reported the polycondensation productof specific thioxanthone-derivatives with amines as the combination ofNorrish type II photoinitiator and a synergist in the same polymer(Polymer, 45 (2004), 5057-5063).

Amine modified polyether imides have been reported by Davidson et al.(Journal of Photochemistry and Photobiology, A: Chemistry (1995), 91(2),153-163), while Angiolini et al. reported acrylate copolymers havingboth an initiating moiety and a tertiary amine (benzoin methyl ethersand tertiary amines : Polymers for Advanced Technologies (1993), 4(6),375-384; benzophenones and tertiary amines: New Polymeric Materials(1987), 1 (1), 63-83; camphorquinone and tertiary amines: MacromolecularChemistry and Physics (2000), 201(18), 2646-2653; thioxanthones andα-morpholinoketones: Polymer (1995), 36(21), 4055-60).

Also in two recent reviews, polymers having both an initiating and aco-initiating moiety have been reported (Corrales et al. in Journal ofPhotochemistry and Photobiology, A: Chemistry (2003), 159(2), 103-114and Carlini et al. in Polymers for Advanced Technologies (1996), 7(5 &6), 379-384).

Although several of these polymers show interesting photochemicalproperties, all of them have a linear geometry. Using thesephotoreactive polymers, the solution viscosity still increases to anundesirable level for a great number of applications with radiationcurable compositions, e.g. ink-jet inks and lacquers.

There is therefore a need to provide radiation curable compositionssuitable for use on food packaging containing a cheap, effectivephotoreactive polymer not being extractable into food or adverselyaffecting the physical properties of the packaging material. Thephotoreactive polymers should be easy to manufacture and should becompatible with a wide range of radiation curable compositions withoutcausing high solution viscosity.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a radiation curablecomposition comprising a new effective photoreactive polymer.

It is a further object of the present invention to provide a radiationcurable composition with a new photoreactive polymer which is easy tomanufacture and compatible with a wide range of radiation curablecompositions.

It is also an object of the present invention to provide a radiationcurable ink-jet ink comprising a photoreactive polymer suitable forink-jet printing on food packaging.

These and other objects of the invention will become apparent from thedescription hereinafter.

SUMMARY OF THE INVENTION

It was surprisingly found that photoreactive polymers having ahyperbranched polymeric core with initiating and co-initiatingfunctional groups thereon were at least as effective as a combination ofboth low molecular weight initiator and co-initiator. Although thephotoreactive polymers had a high functionality, they exhibited alimited influence on viscosity, which widened the options for composingradiation curable ink-jet inks.

Objects of the present invention are with a radiation curablecomposition containing a photoreactive polymer comprising a dendriticpolymer core with at least one initiating functional group and at leastone co-initiating functional group.

The objects of the present invention are also realized with an ink-jetink containing a photoreactive polymer comprising a dendritic polymercore with at least one initiating functional group and at least oneco-initiating functional group.

The objects of the present invention are also realized with a processfor polymerization of monomers, oligomers and/or prepolymers comprisingthe steps of:

-   a) providing a photoreactive polymer, and-   b) admixing the said photoreactive polymer with monomers, oligomers    and/or prepolymers,-   characterized in that said photoreactive polymer comprises a    dendritic polymer core with at least one initiating functional group    and at least one co-initiating functional group.

Further advantages and embodiments of the present invention will becomeapparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The term “actinic radiation” as used in disclosing the presentinvention, means electromagnetic radiation capable of initiatingphotochemical reactions.

The term “ultraviolet radiation” as used in disclosing the presentinvention, means electromagnetic radiation in the wavelength range of 4to 400 nanometers.

The term “UV” is used in disclosing the present application as anabbreviation for ultraviolet radiation.

The term “initiator” as used in disclosing the present invention, meansa Norrish type I initiator, a Norrish type II initiator or a photo-acidgenerator.

The term “Norrish Type I initiator” as used in disclosing the presentinvention, means an initiator which cleaves after excitation, yieldingthe initiating radical immediately.

The term “Norrish type II-initiator” as used in disclosing the presentinvention, means a photoinitiator which is activated by actinicradiation and forms free radicals by hydrogen abstraction or electronextraction from a second compound that becomes the actual initiatingfree radical.

The term “co-initiator” as used in disclosing the present invention,means any molecule capable of transferring a hydrogen to the excitedstate of a Norrish type II-initiator and initiating the radicalpolymerization of a radiation curable composition.

The term “branched polymer” as used in disclosing the present invention,means a polymer chain having branch points that connect three or morepolymeric chain segments.

The term “DB” is used in disclosing the present application as anabbreviation for degree of branching.

The term “dendritic polymer” as used in disclosing the presentinvention, comprises dendrimers and hyperbranched polymers.

The term “hyperbranched polymer” as used in disclosing the presentinvention, means a polymer having a plurality of branch points andmultifunctional branches that lead to further branching with polymergrowth. Hyperbranched polymers are obtained by a one-step polymerizationprocess and form a polydisperse system with varying degrees of branching(DB<100%).

The term “dendrimers” as used in disclosing the present invention, meanswell-defined monodisperse structures in which all branch points are used(DB=100%). Dendrimers are obtained by a multi-step synthesis.

The term “functional group” as used in disclosing the present invention,means an atom or group of atoms, acting as a unit, that has replaced ahydrogen atom in a hydrocarbon molecule and whose presence impartscharacteristic properties to this molecule.

The term “low functionality” as used in disclosing the presentinvention, means having not more than five functional groups.

The term “end group” as used in disclosing the present invention, meansthe terminal group on a branch. In the case of a dendrimer orhyperbranched polymer, a plurality of end groups is present.

The term “initiating functional group” as used in disclosing the presentinvention, means a functional group that renders the molecule capable offunctioning as a initiator.

The term “co-initiating functional group” as used in disclosing thepresent invention, means a functional group that renders the moleculecapable of functioning as a co-initiator.

The term “colorant”, as used in disclosing the present invention, meansdyes and pigments.

The term “dye”, as used in disclosing the present invention, means acolorant having a solubility of 10 mg/L or more in the medium in whichit is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as an inorganic or organic, chromatic or achromatic colouringagent that is practically insoluble in the application medium under thepertaining ambient conditions, hence having a solubility of less than 10mg/L therein.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

The term “acyl group” as used in disclosing the present invention means—(C═O)-aryl groups, —(C═O)-alkyl groups, —(C═O)-heterocyclic groups and—(C═O)-heteroaromatic groups.

The term “aliphatic group” as used in disclosing the present inventionmeans saturated straight chain, branched chain and alicyclic hydrocarbongroups.

The term “aryl group” as used in disclosing the present invention meansan assemblage of cyclic conjugated carbon atoms, which are characterizedby large resonance energies, e.g. benzene, naphthalene and anthracene.The term “aromatic group” is synonymous for the term “aryl group”.

The term “alicyclic hydrocarbon group” means an assemblage of cyclicconjugated carbon atoms, which do not form an aromatic group, e.g.cyclohexane.

The term “substituted” as used in disclosing this invention means thatone or more of the carbon atoms and/or that a hydrogen atom of one ormore of carbon atoms in an aliphatic group, an aromatic group or analicyclic hydrocarbon group, are replaced by an oxygen atom, a nitrogenatom, a sulphur atom, a selenium atom or a tellurium atom. Suchsubstituents include hydroxyl groups, ether groups, carboxylic acidgroups, ester groups, amide groups and amine groups.

The term “heteroaromatic group” means an aromatic group wherein at leastone of the cyclic conjugated carbon atoms is replaced by an oxygen atom,a nitrogen atom, a phosphorous atom, a silicon atom, a sulfur atom, aselenium atom or a tellurium atom.

The term “heterocyclic group” means an alicyclic hydrocarbon groupwherein at least one of the cyclic conjugated carbon atoms is replacedby an oxygen atom, a nitrogen atom, a phosphorous atom, a silicon atom,a sulfur atom, a selenium atom or a tellurium atom.

Dendritic Polymers

The photoreactive polymer for use in a radiation curable compositionaccording to the present invention contains a core of dendritic polymer,e.g. a dendrimer or a hyperbranched polymer. The photoreactive polymerfor use in a radiation curable composition according to the presentinvention has preferably a core of hyperbranched polymer.

Dendrimers are characterized by cascade-type branching, i.e. abranch-on-branch topology. Dendrimers are prepared in a multi-stepsynthesis, based on repeated branching and deprotection schemes asdisclosed by NEWCOME, G. R., et al. Dendritic Molecules: Concepts,Synthesis, Perspectives. VCH: WEINHEIM, 2001. Dendrimer synthesisstrategies generally aim at fully branched polymers, although inrecently reported examples a fraction of imperfectly branched specieshas been reported as (undesired) side-products. Suitable dendrimers arepolyamidoamine (PAMAM) Starburst™ dendrimers as disclosed by TOMALIA, etal. A new class of polymers: starburst-dendritic macromolecules. Polym.J. 1985, vol. 17, p. 117. and convergently prepared polybenzyletherdendrimers as disclosed by HAWKER, et al. Preparation of polymers withcontrolled molecular architecture. A new convergent approach todendritic macromolecules. J. Am. Chem. Soc. 1990, vol. 112, p. 7638.

Synthesis

The stepwise preparation, which represents the only strategy for thepreparation of dendrimers at present, is a limiting factor for mostapplications. In contrast to dendrimers, the structurally irregular, i.e. hyperbranched polymers are obtained in a single synthetic step.

In the present invention both polymers obtained by strict hyperbranchingpolymerization as well as polymers obtained by subcriticalpolymerization of e.g. A₂+B₃ types of monomers are considered ashyperbranched.

A stringent criterion for strict hyperbranching polymerization is thatno critical conversion p_(c) may exist, at which gelation of the systemoccurs and a network structure is obtained, as disclosed by BURCHARD,W., et al. Solution properties of branched macromolecules. Advances inPolymer Science. 1999, vol. 143, no. II, p. 113-194.

Hyperbranched materials can thus be obtained by polycondensation of AB₂or AB_(m)-type monomers with complementary functionality's A and B, theonly coupling reaction in the system being the linking of A and B.Details on this type of polyfunctional polycondensation are disclosed byFLORY, P. J., et al. Molecular size distribution in three-dimensionalpolymers. VI. Branched polymer containing A-R-Bf-1-type units. Journalof the American Chemical Society. 1952, vol. 74, p. 2718-2723.

U.S. Pat. No. 4,857,630 (DU PONT) and KIM, Y. H., et al. Hyperbranchedpolyphenylenes. Polymer Preprints (American Chemical Society, Divisionof Polymer Chemistry). 1988, vol. 29, no. 2, p. 310-311. disclosesynthesis methods for preparing hyperbranched polyphenylenes.

Methods for preparing hyperbranched polymers based on polycondensationof AB₂-monomers are further disclosed in U.S. Pat. No. 5,196,502(KODAK), U.S. Pat. No. 5,225,522 (KODAK) and U.S. Pat. No. 5,214,122(KODAK).

Another suitable approach for preparing hyperbranched polymer structuresis the polymerization of linear AB*-type inimers. Inimers are compoundsthat possess a common, linearly polymerizable moiety, such as a vinylgroup or a strained cyclic component as well as an initiating group inthe same molecule. Cyclic inimers have been used in the preparation ofhyperbranched structures by VANDENBERG, E. J., et al. Polymerization ofglycidol and its derivatives: a new rearrangement polymerization.Journal of Polymer Science. 1985, vol. 23, no. 4, p. 915-949., FRECHET,J., et al. Selfcondensing vinyl polymerization: an approach to dendriticmaterials. Science (Wash., D. C.). 1995, vol. 269, no. 5227, p.1080-1083. and EP 791021 A (CORNELL RES FOUNDATION INC).

Linear AB type compounds, commonly called “linear co-monomers” as wellas poly-B-functional compounds of B_(f)-structure may be present,commonly designated “core molecules”. An overview of the structuralpossibilities as well as a stringent definition for the degree ofbranching DB, a relevant parameter for the functionality ofhyperbranched polymers is disclosed by HOLTER, et al. Degree ofbranching in hyperbranched polymers. Acta Polymerica. 1997, vol. 23, no.48, p. 30-35., HOLTER, et al. Degree of branching (DB) in hyperbranchedpolymers. Part 2. Enhancement of the DB. Scope and limitations. ActaPolymerica. 1997, vol. 48, no. 8, p. 298-309. and FREY, H., et al.Degree of branching in hyperbranched polymers. Part 3. Copolymerizationof ABm monomers with AB and ABn monomers. Journal of Polymer Science.1999, vol. 50, no. 2-3, p. 67-76.

The state of the art in hyperbranched polymer research has been reviewedin:

-   (a) JIKEI, M., et al. Hyperbranched polymers: a promising new class    of materials. Progress in Polymer Science. 2001, vol. 26, no. 8, p.    1233-1285.-   (b) NEWCOME, G. R., et al. Dendritic Molecules: Concepts, Synthesis,    Perspectives. VCH: WEINHEIM, 2001.-   (c) KIM, Y., et al. Hyperbranched polymers 10 years after. Journal    of Polymer Science, Part A: Polymer Chemistry. 1998, vol. 36, no.    11, p. 1685-1698.-   (d) VOIT, B., et al. New developments in hyperbranched polymers.    Journal of Polymer Science, Part A: Polymer Chemistry. 2000, vol.    38, no. 14, p. 2505-2525.-   (e) SUNDER, A., et al. Controlling the growth of polymer trees:    concepts and perspectives for hyperbranched polymers. Chemistry—A    European Journal. 2000, vol. 6, no. 14, p. 2499-2506.-   From these reviews, it is evident that hyperbranched polymers are    clearly distinguishable from the regularly branched dendrimers as    well as from branched structures based on A₂+B₃ polymerization of    two polyfunctional monomers that inevitably leads to gelation, i.e.    network formation, if polymerization is not stopped at a subcritical    level.

Hyperbranched polymers commonly possess broad molecular weightdistribution. The polydispersity M_(w)/M_(n) is usually greater than 5and more often greater than 10. Recently new concepts have beenintroduced that are based on the slow addition of AB₂ or latent AB₂monomers of suitable reactivity to a polyfunctional (B_(f)) coremolecule. The procedure is disclosed by RADKE, W., et al. Effect ofCore-Forming Molecules on Molecular Weight Distribution and Degree ofBranching in the Synthesis of Hyperbranched Polymers. Macromolecules.1998, vol. 31, no. 2, p. 239-248. and HANSELMANN, R., et al.Hyperbranched Polymers Prepared via the Core-Dilution/Slow AdditionTechnique: Computer Simulation of Molecular Weight Distribution andDegree of Branching. Macromolecules. 1998, vol. 31, no. 12, p.3790-3801.

Hyperbranched Polymer Core

The size of the hyperbranched polymer core for a photoreactive polymerfor use in a radiation curable composition according to the presentinvention is determined by the selected application. Most ink-jetapplications require ink-jet inks with a low viscosity, usually lowerthan 100 mPa.s. Hence for ink-jet applications, the hyperbranchedpolymers preferably have a M_(w) smaller than 100,000, more preferablysmaller than 50,000 and most preferably smaller than 20,000.

The hyperbranched polymer core for a photoreactive polymer for use in aradiation curable composition according to the present invention ispreferably obtained by the method of slow monomer addition. This resultsin a narrow polydispersity of the hyperbranched polymers. Particularlypreferred in the present invention are hyperbranched polymers with apolydispersity M_(w)/M_(n) smaller than 3.

Suitable hyperbranched polymer cores are disclosed in GAO, C., et al.Hyperbranched polymers: from synthesis to applications. Progress inPolymer Science. 2000, vol. 29, no. 3, p. 183-275.

Other suitable hyperbranched polymer cores are given in Table 1, withoutbeing limited thereto. TABLE 1 PC-1

PC-2

PC-3

PC-4

PC-5

PC-6

PC-7

PC-8

The hyperbranched polymer core can be used as a core for terminalgrafting before derivatization with a reactive co-initiator andinitiator (derivative). This yields a hyperbranched multiple arm graftstar copolymer, which is also considered to be a hyperbranched polymercore. Suitable examples of this type of polymers are disclosed inSUNDER, A., et al. Hyperbranched Polyether-Polyols Based onPolyglycerol: Polarity Design by Block Copolymerization with PropyleneOxide. Polyglycerol: Polarity Design by Block Copolymerization withPropylene Oxide. Macromolecules. 2000, vol. 22, no. 3, p. 309-314. andMAIER, S., et al. Synthesis of poly(glycerol)-block-poly(methylacrylate) multi-arm star polymers. Macromolecular Rapid Communications.2000, vol. 21, no. 5, p. 226-230.

Any hyperbranched polymer can be used as a polymer core in thephotoreactive polymers, but hyperbranched polyglycidols or hyperbranchedcopolymers of glycidol and other epoxides are particularly preferred.They can be readily prepared with a narrow molecular weight distributionin a single step procedure from commercially available monomers over abroad range of molecular weights. The reaction of these core polymerswith at least one co-initiator or co-initiator derivative and with atleast one initiator or initiator derivative yields a particularlypreferred class of hyperbranched photoreactive polymers for use in aradiation curable composition according to the present invention.

Branched polyols based on glycerol units are usually prepared byreacting glycidol with a hydrogen-containing compound (e.g., glycerol)in the presence of inorganic acids as disclosed by JP 61043627 A (DAICELCHEM IND.) or organic acids as disclosed by JP 58198429 A (NIPPON YUSHI)as catalyst. The polymerization of glycidol can also be achieved viacationic polymerization using cationic initiators, such as BF₃ asdisclosed by TOKAR, R., et al. Cationic polymerisation of glycidol:coexistence of the activated monomer and active chain end mechanism.Macromolecules. 1994, vol. 27, p. 320. and DWORAK, A., et al. Cationicpolymerization of glycidol. Polymer structure and polymerizationmechanism. Macromolecular Chemistry and Physics. 1995, vol. 196, no. 6,p. 1963-1970. However, a cationic polymerization method leads tohyperbranched polymer with a polydispersity larger than 3 and molecularweights can not be controlled.

A suitable procedure for the preparation of hyperbranched polyglycerolswith a controlled molecular weight is disclosed in DE 19947631 A(BAYER). This is achieved by adding glycidol diluted in a hydrocarbon oran ether to a suitable polyol initiator that is dissolved in diglyme oranother hydrocarbon as disclosed in SUNDER, A., et al. ControlledSynthesis of Hyperbranched Polyglycerols by Ring-Opening MultibranchingPolymerization. Macromolecules. 1999, vol. 92, no. 13, p. 4240-4246. Themonomer is added as solution containing between 20 and 99.9 wt %, e.g.,60%-90% THF. Full incorporation of an initiator is promoted by the useof a polyfunctional initiator.

Photoreactive Polymers

The photoreactive polymer for use in a radiation curable compositionaccording to the present invention comprises a dendritic polymer corewith at least one initiating functional group and at least oneco-initiating functional group.

In a first embodiment, the photoreactive polymer for use in a radiationcurable composition according to the present invention a dendriticpolymeric core derivatized with at least one photoinitiator orderivative thereof and at least one co-initiator or derivative thereof.

In a second embodiment, the co-initiator may be part of the dendriticpolymeric core, which is only derivatized with a photoinitiator orderivative thereof.

The photoreactive polymer may be further derivatized with otherfunctional groups such as a compatibilizing moiety. For example, thecompatibilizing moiety may introduce ionic groups onto the dendriticpolymer core so that photoreactive polymer can be easily dissolved inwater or an aqueous solution such as a water based radiation curableink-jet ink.

The photoreactive polymers have preferably at least three co-initiatingfunctional groups on the dendritic polymer core, more preferably atleast five co-initiating functional groups on the dendritic polymercore, and most preferably at least seven co-initiating functional groupson the dendritic polymer core.

The photoreactive polymers have preferably at least three initiatingfunctional groups on the dendritic polymer core, more preferably atleast five initiating functional groups on the dendritic polymer core,and most preferably at least seven initiating functional groups on thedendritic polymer core.

Any photo-initiating moiety known in the prior art can be used in thepresent invention. The photo-initiating moiety for the photoreactivepolymer for use in a radiation curable composition according to thepresent invention is preferably selected from the group consisting of aNorrish type I-initiator, a Norrish type II-initiator and a photoacid.More preferably, the photo-initiating moiety is a Norrish typeII-photoinitiator.

A preferred Norrish type II-initiator is selected from the groupconsisting of benzophenones, thioxanthones, 1,2-diketones andanthraquinones.

Suitable Norrish type II-initiators are disclosed in CRIVELLO, J. V., etal. VOLUME III: Photoinitiators for Free Radical Cationic & AnionicPhotopolymerization. 2ndth edition. Edited by BRADLEY, G. London, UK:John Wiley and Sons Ltd, 1998. p. 287-294.

Suitable examples of photo-initiating moieties capable of reacting witha dendritic polymer core are given in Table 2 without being limitedthereto. TABLE 2 INI-1

INI-2

INI-3

INI-4

INI-5

INI-6

INI-7

INI-8

INI-9

INI-10

INI-11

INI-12

INI-13

INI-14

Any co-initiating moiety known in the prior art can be used toderivative the dendritic polymeric core. In a more preferred embodiment,the co-initiating moiety is selected from the group consisting of analiphatic amine, an aromatic amine and a thiol. In an even morepreferred embodiment, the co-initiating moiety is selected from thegroup consisting of a tertiary amine, a 4-dialkylaminobezoic acidderivative and a heterocyclic thiol.

Suitable examples of co-initiating moieties capable of reacting with adendritic polymeric core are given in Table 3, without being limitedthereto. TABLE 3 SYN-1

SYN-2

SYN-3

SYN-4

SYN-5

SYN-6

SYN-7

SYN-8

SYN-9

SYN-10

SYN-11

SYN-12

SYN-13

SYN-14

SYN-15

SYN-16

The dendritic polymer core can be fully or partially derivatized.

It is evident for those skilled in the art that many types ofderivatization chemistry can be used to derivatize the dendriticpolymeric core with photo-initiating moieties and the co-initiatingmoieties. In the case of hyperbranched polyglycidols, esterification andetherification are particularly preferred.

In a preferred embodiment, the photoreactive polymers are furtherderivatized with a compatibilizing group. A compatibilizing group isdefined as a functional group making the photoreactive polymer moresoluble in a specific radiation curable composition.

Suitable examples of compatibilizing groups are given in Table 4,without being limited thereto. TABLE 4 Compatibilizer R—COOH C-1

C-2

C-3

C-4

C-5

C-6

C-7

C-8

C-9

C-10

Suitable examples of photoreactive polymers according to the firstembodiment are given below, without being limited thereto. Thestructures given represent one molecular weight with one degree ofderivatization out of the distribution found in each prepared sample.The structures represent a more generic structure, as a specific examplefor different molecular weights and degrees of substitution. It isobvious for those skilled in the art that each polymer sample is amixture of similar individual compounds, differing in both molecularweight and degree of substitution and that the chemistry can be extendedover a wide range of molecular weights.

Suitable photoreactive polymers for use in a radiation curablecomposition according to the present invention, having a hyperbranchedpolyester core are disclosed in Table 5. Structure of a hyperbrachedpolyester core: TABLE 5

Photoreactive Initiator moiety Co-initiator moiety CompatibilizerPolymer R1-COOH R2-COOH R3-COOH PES-1 INI-1 SYN-1 C-10 PES-2 INI-2 SYN-5C-1 PES-3 INI-11 SYN-2 C-6 PES-4 INI-3 SYN-10 C-9 PES-5 INI-6 SYN-16C-10 PES-6 INI-4 SYN-1 C-3 PES-7 INI-5 SYN-2 C-6 PES-8 INI-10 SYN-1 C-5

Suitable photoreactive polymers for use in a radiation curablecomposition according to the present invention, have a hyperbranchedpolyester-amine core are disclosed in Table 6. Structure of ahyperbranched polyester-amine core: TABLE 6

Photoreactive Initiator moiety Co-initiator moiety Compatibilizerpolymer R1-COOH R2-COOH R3-COOH PESA-1 INI-1 SYN-1 C-10 PESA-2 INI-3SYN-5 C-1 PESA-3 INI-10 SYN-2 C-10 PESA-4 INI-5 SYN-5 C-10 PESA-5 INI-11SYN-1 C-6 PESA-6 INI-4 SYN-2 C-6 PESA-7 INI-1 SYN-12 C-3 PESA-8 INI-12SYN-1 C-3

Suitable photoreactive polymers for use in a radiation curablecomposition according to the present invention, have a hyperbranchedpolyether core are disclosed in Table 7. Structure of a hyperbranchedpolyether core: TABLE 7

Photoreactive Initiator moiety Co-initiator moiety Compatibilizerpolymer R1-COOH R2-COOH R3-COOH PE-1 INI-1 SYN-5 C-10 PE-2 INI-2 SYN-1C-10 PE-3 INI-2 SYN-5 C-10 PE-4 lNI-1 SYN-1 C-10 PE-5 INI-12 SYN-2 C-1PE-6 INI-11 SYN-10 C-6 PE-7 INI-3 SYN-2 C-3 PE-8 INI-4 SYN-5 C-9 PE-9INI-13 SYN-10 C-6 PE-10 INI-14 SYN-1 C-1

In a second embodiment of the present invention, the co-initiator ispart of the hyperbranched polymeric core and the end groups arederivatized with a photo-initiator or derivative thereof. Thehyperbranched polymeric core can be both a regular hyperbranched polymersuch as a dendrimer or a random hyperbranched polymer.

Suitable examples of photoreactive polymers for use in a radiationcurable composition according to the present invention, having adendritic polymeric core of a dendrimer or a dendritic polymeric core ofa hyperbranched polymer are given below, without being limited thereto.

Photoreactive polymers according to the second embodiment having adendritic polymeric core of a dendrimer are disclosed in Table 8.Structure of a dendritic polymeric core of a dendrimer: TABLE 8

Initiator moiety Compatibilizer Photoreactive polymer R1-COOH R1-COOHDENDRI-1 INI-1 C-10 DENDRI-2 INI-2 C-6 DENDRI-3 INI-10 C-1

Photoreactive polymers according to the second embodiment having adendritic polymeric core of a hyperbranched polymer are disclosed inTable 9. Structure of a dendritic polymeric core of a hyperbranchedpolymer: TABLE 9

Photoreactive Initiator moiety Compatibilizer polymer R1-COOH R2-COOHAM-i INI-1 C-10 AM-2 INI-2 C-6 AM-3 INI-10 C-1Radiation Curable Composition

The radiation curable composition according to the present invention canbe any radiation curable composition such as a varnish, a lacquer, aprinting ink and a radiation curable ink-jet ink.

The radiation curable ink-jet ink is preferably jetted on an ink-jetrecording element chosen from the group consisting of paper, coatedpaper, polyolefin coated paper, cardboard, wood, composite boards,plastic, coated plastic, canvas, textile, metal, glasses, plant fibreproducts, leather, magnetic materials and ceramics.

The radiation curable inkjet ink jetted on an ink-jet recording elementcreates an uncured printed image. This printed image is cured byradiation or electron beam exposure. A preferred means of radiationcuring is ultraviolet light.

A radiation-curable composition according to the present inventioncontains at least two components: (i) a radiation-curable compound, and(ii) a photoreactive polymer. A preferred amount of the photoreactivepolymer is 1-50 wt % of the total radiation-curable composition weight,and more preferably 1 to 25 wt % of the total radiation-curablecomposition weight. In a preferred embodiment this radiation-curablecomposition exhibits characteristics suitable for jetting by an ink-jetprinter to provide a clear layer on the ink-jet recording element. Inanother preferred embodiment, the radiation curable compositionexhibiting characteristics suitable for jetting by an ink-jet printercontains particles to provide a white layer on the ink-jet recordingelement.

Radiation-Curable Ink-Jet Ink

A radiation-curable ink-jet ink according to the present inventioncontains at least three components: (i) a radiation-curable compound,(ii) a colorant (i.e. pigment or dye) and (iii) a photoreactive polymer.A preferred amount of the photoreactive polymer is 1-50 wt % of thetotal ink weight, and more preferably 1 to 25 wt % of the total inkweight.

The radiation-curable compound can be selected from monomers and/oroligomers that can be polymerized by a curing means of an ink-jetprinter.

The radiation-curable ink-jet ink may contain a polymerization inhibitorto restrain polymerization by heat or actinic radiation. It is preferredto add an inhibitor during preparation of the ink-jet ink.

The radiation-curable ink-jet ink may further contain at least one resinin order to obtain a stable dispersion of the colorant in the ink-jetink.

The radiation-curable ink-jet ink preferably further contains at leastone surfactant.

The radiation-curable ink-jet ink preferably further contains at leastone solvent.

The radiation-curable ink-jet ink preferably further contains at leastone biocide.

An ink-jet printer generally uses a radiation-curable ink-jet ink setconsisting of a plurality of radiation-curable ink-jet inks.

Radiation-Curable Compounds

The radiation curable ink-jet ink contains monomers and/or oligomers,which are polymerized by the curing means of the ink-jet printer.

Monomers, oligomers or prepolymers may possess different degrees offunctionality, and a mixture including combinations of mono-, di-,tri-and higher functionality monomers, oligomers and/or prepolymers maybe used. These components are curable, typically photo-curable, e.g. UVcurable, and should adhere to the ink-receiver surface after printingand serve to bind the colorant. A mixture of two or more monomers of thesame functionality is preferred, with particularly preferred a mixtureof two di-functional monomers.

The viscosity of the radiation curable ink-jet ink can be adjusted byvarying the ratio between the monomers and oligomers.

Any method of conventional radical polymerization, photo-curing systemusing photo acid or photo base generator, or photo induction alternatingcopolymerization may be employed. In general, radical polymerization andcationic polymerization are preferred, and photo induction alternatingcopolymerization needing no initiator may also be employed. Furthermore,a hybrid system of combinations of these systems is also effective.

Cationic polymerization is superior in effectiveness due to lack ofinhibition of the polymerization by oxygen, however it is slow andexpensive. If cationic polymerization is used, it is preferred to use anepoxy compound together with an oxetane compound to increase the rate ofpolymerization. Radical polymerization is the preferred polymerizationprocess.

Any polymerizable compound commonly known in the art may be employed.Particularly preferred for use as a radiation-curable compound in theradiation curable ink-jet ink, are monofunctional and/or polyfunctionalacrylate monomers, oligomers or prepolymers, such as isoamyl acrylate,stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate,isoamylstyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycolacrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethylhexahydrophthalicacid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate,methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate,methoxypropylene glycol acrylate, phenoxyethyl acrylate,tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate,vinyl ether acrylates such as described in U.S. Pat. No. 6,310,115(AGFA), 2-(vinyloxy)ethylacrylate, 2-acryloyloxyethylsuccinic acid,2-acryloyxyethylphthalic acid, 2-acryloxyethyl-2-hydroxyethyl-phthalicacid, lactone modified flexible acrylate, and t-butylcyclohexylacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate,dipropylene glycoldiacrylate, tripropylene glycol diacrylate, polypropylene glycoldiacrylate, 1,4butanediol diacrylate, 1,6hexanediol diacrylate,1,9nonanediol diacrylate, neopentyl glycol diacrylate,dimethylol-tricyclodecane diacrylate, bisphenol A EO (ethylene oxide)adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate,hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentylglycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate andpolytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EOmodified trimethylolpropane triacrylate, tri (propylene glycol)triacrylate, caprolactone modified trimethylolpropane triacrylate,pentaerythritol triacrylate, pentaerithritol tetraacrylate,pentaerythritolethoxy tetraacrylate, dipentaerythritol hexaacrylate,ditrimethylolpropane tetraacrylate, glycerinpropoxy triacrylate,caprolactam modified dipentaerythritol hexaacrylate, N-vinylamide suchas N-vinylcaprolactam or N-vinylformamide; or acrylamide or asubstituted acrylamide such as acryloylmorpholine; and aminofunctionalized polyetheracrylates such as described in U.S. Pat. No.6,300,388 (AGFA).

Furthermore, methacrylates corresponding to the above-mentionedacrylates may be used with these acrylates. Of the methacrylates,methoxypolyethylene glycol methacrylate, methoxytriethylene glycolmethacrylate, 4-(vinyloxy)butylmethacrylate, vinyl ether acrylates suchas described in U.S. Pat. No. 6,310,115 (AGFA), hydroxyethylmethacrylate, phenoxyethyl methacrylate, cyclohexyl methacrylate,tetraethylene glycol dimethacrylate, and polyethylene glycoldimethacrylate are preferred due to their relatively high sensitivityand higher adhesion to an ink-receiver surface.

Furthermore, the ink-jet inks may also contain polymerizable oligomers.Examples of these polymerizable oligomers include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Colorants

Colorants may be dyes, but are preferably pigments or a combinationthereof. Organic and/or inorganic pigments may be used.

The pigment particles should be sufficiently small to permit free flowof the ink through the ink-jet printing device, especially at theejecting nozzles which usually have a diameter ranging from 10 μm to 50μm. The particle size influences also the pigment dispersion stability.It is also desirable to use small particles for maximum colour strength.The particles of the pigment dispersed in the ink-jet ink should have aparticle size of less than 10 μm, preferably less than 3 μm, and mostpreferably less than 1 μm. The average particle size of pigmentparticles is preferably 0.05 to 0.5 μm.

Suitable pigments include as red or magenta pigments: Pigment Red 3, 5,19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53: 1, 57:1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108,112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184,185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, and88; as blue or cyan pigments: Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3,15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, and 60; as green pigments:Pigment green 7, 26, 36, and 50; as yellow pigments: Pigment Yellow 1,3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109,110, 128, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 177, 180,185, and 193; as white pigment: Pigment White 6, 18, and 21.

Furthermore, the pigment may be chosen from those disclosed by HERBST,W. et al. Industrial Organic Pigments, Production, Properties,Applications. 2nd edition. VCH, 1997.

Most preferred pigments are Pigment Yellow 1, 3, 128, 109, 93, 17, 14,10, 12, 13, 83, 65, 75, 74, 73, 138, 139, 154, 151, 180, 185; PigmentRed 122, 22, 23, 17, 210, 170, 188, 185, 146, 144, 176, 57:1, 184, 202,206, 207; Pigment Blue 15:3, Pigment Blue 15:2, Pigment Blue 15:1,Pigment Blue 15:4, Pigment Blue 15:6, Pigment Blue 16 and Pigment Violet19.

Carbon black is usually used as the colouring material in black ink.

Suitable black pigment materials include carbon blacks such as PigmentBlack 7 (e.g. Carbon Black MA8™ from MITSUBISHI CHEMICAL), Regal™ 400R,Mogul™ L, Elftex™ 320 from CABOT Co., or Carbon Black FW18, SpecialBlack 250, Special Black 350, Special Black 550, Printex™ 25, Printex™35, Printex™ 55, Printex™ 90, Printex™ 150T from DEGUSSA.

Additional examples of suitable pigments are disclosed in U.S. Pat. No.5,389,133 (XEROX).

The pigment is present in the range of 0.1 to 10 wt %, preferably in therange 1 to 5 wt % based on the total weight of the radiation curableink-jet ink.

Dyes suitable for the radiation curable ink-jet ink include direct dyes,acidic dyes, basic dyes and reactive dyes.

Suitable direct dyes for the radiation curable ink-jet ink include:

-   C.I. Direct Yellow 1, 4, 8, 11, 12, 24, 26, 27, 28, 33, 39, 44, 50,    58, 85, 86, 100, 110, 120, 132, 142, and 144-   C.I. Direct Red 1, 2, 4, 9, 11, 134, 17, 20, 23, 24, 28, 31, 33, 37,    39, 44, 47, 48, 51, 62, 63, 75, 79, 80, 81, 83, 89, 90, 94, 95, 99,    220, 224, 227 and 343-   C.I. Direct Blue 1, 2, 6, 8, 15, 22, 25, 71, 76, 78, 80, 86, 87, 90,    98, 106, 108, 120, 123, 163, 165, 192, 193, 194, 195, 196, 199, 200,    201, 202, 203, 207, 236, and 237-   C.I. Direct Black 2, 3, 7, 17, 19, 22, 32, 38, 51, 56, 62, 71, 74,    75, 77, 105, 108, 112, 117, and 154

Suitable acidic dyes for the radiation curable ink-jet ink include:

-   C.I. Acid Yellow 2, 3, 7, 17, 19, 23, 25, 20, 38, 42, 49, 59, 61,    72, and 99-   C.I. Acid Orange 56 and 64-   C.I. Acid Red 1, 8, 14, 18, 26, 32, 37, 42, 52, 57, 72, 74, 80, 87,    115, 119, 131, 133, 134, 143, 154, 186, 249, 254, and 256-   C.I. Acid Violet 11, 34, and 75-   C.I. Acid Blue 1, 7, 9, 29, 87, 126, 138, 171, 175, 183, 234, 236,    and 249-   C.I. Acid Green 9, 12, 19, 27, and 41-   C.I. Acid Black 1, 2, 7, 24, 26, 48, 52, 58, 60, 94, 107, 109, 110,    119, 131, and 155

Suitable reactive dyes for the radiation curable ink-jet ink include:

-   C.I. Reactive Yellow 1, 2, 3, 14, 15, 17, 37, 42, 76, 95, 168, and    175-   C.I. Reactive Red 2, 6, 11, 21, 22, 23, 24, 33, 45, 111, 112, 114,    180, 218, 226, 228, and 235-   C.I. Reactive Blue 7, 14, 15, 18, 19, 21, 25, 38, 49, 72, 77, 176,    203, 220, 230, and 235-   C.I. Reactive Orange 5, 12, 13, 35, and 95-   C.I. Reactive Brown 7, 11, 33, 37, and 46-   C.I. Reactive Green 8 and 19-   C.I. Reactive Violet 2, 4, 6, 8, 21, 22, and 25-   C.I. Reactive Black 5, 8, 31, and 39

Suitable basic dyes for the radiation curable ink-jet ink include:

-   C.I. Basic Yellow 11, 14, 21, and 32-   C.I. Basic Red 1, 2, 9, 12, and 13-   C.I. Basic Violet 3, 7, and 14-   C.I. Basic Blue 3, 9, 24, and 25

Dyes can only manifest the ideal colour in an appropriate range of pHvalue. Therefore, the radiation curable ink-jet ink preferably furthercomprises a pH buffer, such as potassium hydroxide (KOH).

Inhibitors

Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol may also be used. Ofthese, a phenol compound having a double bond in molecules derived fromacrylic acid is particularly preferred due to its having apolymerization-restraining effect even when heated in a closed,oxygen-free environment. Suitable inhibitors are, for example,Sumilizer™ GA-80, Sumilizer™ GM and Sumilizer™ GS produced by SumitomoChemical Co., Ltd; Genorad™ 16 available from RAHN.

Since excessive addition of these polymerization inhibitors will lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization be determined prior to blending. The amountof a polymerization inhibitor is generally between 200 and 20,000 ppm ofthe total ink weight.

Resins

The radiation curable ink-jet ink may further contain a resin, alsocalled a pigment stabilizer or dispersant, in order to obtain a stabledispersion of the pigment(s) in the ink-jet ink.

The pigments may be added to the radiation curable ink-jet ink as adispersion comprising a dispersant.

Suitable resins: petroleum type resins (e.g., styrene type, acryl type,polyester, polyurethane type, phenol type, butyral type, cellulose type,and rosin); and thermoplastic resins (e.g., vinyl chloride, vinylacetatetype). Concrete examples of these resins include acrylate copolymers,styrene-acrylate copolymers, acetalized and incompletely saponifiedpolyvinyl alcohol, and vinylacetate copolymers. Commercial resins areknown under the tradenames Solsperse™ 32000 and Solsperse™ 39000available from AVECIA, EFKA™ 4046 available from EFKA CHEMICALS BV,Disperbyk™ 168 available from BYK CHEMIE GMBH.

A detailed list of non-polymeric as well as some polymeric dispersantsis disclosed by MC CUTCHEON. Functional Materials, North AmericanEdition. Glen Rock, N.J.: Manufacturing Confectioner Publishing Co.,1990. p. 110-129.

Typically resins are incorporated at 2.5% to 200%, more preferably at50% to 150% by weight of the pigment.

Surfactants

The radiation curable ink-jet ink may contain at least one surfactant.The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionicand are usually added in a total quantity below 20 wt % based on thetotal ink weight and particularly in a total below 10 wt % based on thetotal ink weight.

A fluorinated or silicone compound may be used as a surfactant, however,a potential drawback is extraction by food from ink-jet food packagingmaterial because the surfactant does not cross-link. It is thereforepreferred to use a copolymerizable monomer having surface-activeeffects, for example, silicone-modified acrylates, silicone modifiedmethacrylates, fluorinated acrylates, and fluorinated methacrylates.

Solvents

The radiation curable ink-jet ink may contain as a solvent, water and/ororganic solvents, such as alcohols, fluorinated solvents and dipolaraprotic solvents, the solvent preferably being present in aconcentration between 10 and 80 wt %, particularly preferably between 20and 50 wt %, each based on the total weight of the radiation curableink-jet ink.

However, the radiation curable ink-jet ink preferably does not containan evaporable component, but sometimes, it can be advantageous toincorporate an extremely small amount of an organic solvent in such inksto improve adhesion to the ink-receiver surface after UV curing. In thiscase, the added solvent can be any amount in the range which does notcause problems of solvent resistance and VOC, and preferably 0.1-5.0 wt%, and particularly preferably 0.1-3.0 wt %, each based on the totalweight of the radiation curable ink-jet ink

Suitable organic solvents include alcohol, aromatic hydrocarbons,ketones, esters, aliphatic hydrocarbons, higher fatty acids, carbitols,cellosolves, higher fatty acid esters. Suitable alcohols include,methanol, ethanol, propanol and 1-butanol, 1-pentanol, 2-butanol,t.-butanol. Suitable aromatic hydrocarbons include toluene, and xylene.Suitable ketones include methyl ethyl ketone, methyl isobutyl ketone,2,4-pentanedione and hexafluoroacetone. Also glycol, glycolethers,N-methylpyrrolidone, N,N-dimethylacetamid, N,N-dimethylformamid may beused.

Biocides

Suitable biocides for the radiation curable ink-jet ink include sodiumdehydroacetate, 2-phenoxyethanol, sodium benzoate, sodiumpyridinethion-1-oxide, ethyl p-hydroxybenzoate and1,2-benzisothiazolin-3-one and salts thereof. A preferred biocide forradiation curable ink-jet ink is Proxel™ GXL available from ZENECACOLOURS.

A biocide is preferably added in an amount of 0.001 to 3 wt %, morepreferably 0.01 to 1.00 wt. %, each based on the radiation curableink-jet ink.

Preparation of a Radiation Curable Ink-Jet Ink

A dispersion of colorant for use in the radiation curable ink-jet inkmay be prepared by mixing, milling and dispersion of colorant and resin.Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a colloid mill, a high-speeddisperser, double rollers, a bead mill, a paint conditioner, and triplerollers. The dispersions may also be prepared using ultrasonic energy.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and as much aspossible under light conditions in which UV-light has been substantiallyexcluded.

The radiation curable ink-jet ink may be prepared using separatedispersions for each colorant, or alternatively several pigments may bemixed and co-milled in preparing the dispersion.

EXAMPLES

The present invention will now be described in detail by way of Exampleshereinafter.

Measurement Methods

1. Curing Speed

The percentage of the maximum output of the lamp was taken as a measurefor curing speed, the lower the number the higher curing speed. A samplewas considered as fully cured at the moment scratching with a Q-tipcaused no visual damage.

2. Viscosity

The viscosity of the radiation curable composition was measured with aBrookfield DV-II+ viscometer at 25° C. and shear rate 3 RPM.

Materials

All materials used in the following examples were readily available fromAldrich Chemical Co. (Belgium) unless otherwise specified. The “water”used in the examples was deionized water. The following materials wereused:

-   DPGDA™ is a difunctional acrylate monomer available from UCB.-   Sartomer™ SR351 is a trifunctional acrylate monomer available from    BASF.-   Quantacure™ EHA available from RAHN AG.-   The hyperbranched polyglycidols PG₁₇, PG₃₃, PG₈₃ and PG₁₇₉ are    available from HYPERPOLYMERS GMBH, Freiburg, Germany Boltorn™ H20    available from PERSTORP.-   PET is the abbreviation for poly(ethylene) terephthalate. Unsubbed    PET substrate with on the backside an anti-blocking layer with    anti-static properties is available from AGFA-GEVAERT as P125C    PLAIN/ABAS.

Example 1

This example illustrates the synthesis of a hyperbranched polyglycidolcore derivatized with benzophenone and piperidine.

The photoreactive polymers IS-1 to IS-4 were prepared and can berepresented by generalized formula IS-A.

-   Generalized formula IS-A:    wherein,-   PG represents a hyperbranched polyglycidol core-   x represents the average number of terminal hydroxyl groups in the    starting polyglycidol

The hyperbranched polyglycidols selected for this example had differentmolecular weights:

-   PG₁₇: a hyperbranched polyglycidol with 17 hydroxyl groups on    average;-   PG₃₃: a hyperbranched polyglycidol with 33 hydroxyl groups on    average;-   PG₈₃: a hyperbranched polyglycidol with 83 hydroxyl groups on    average; and-   PG₁₇₉: a hyperbranched polyglycidol with 179 hydroxyl groups on    average.

The synthesis of IS-1 to IS-4 can be represented by the followingreaction scheme:

The photoreactive polymers IS-1 to IS-4 were prepared according to Table10, which mentions the ratio of the different groups acylated onto eachstarting polyglycidol. TABLE 10 Photo- reactive polymer x PPA MEEA BPGeneral formula IS-1 17 4.6 8.1 4.3 PG₁₇BP_(4.3)PPA_(4.6)MEEA_(8.1) IS-233 8.9 15.1 8.2 PG₃₃BP_(8.2)PPA_(8.9)MEEA_(15.9) IS-3 83 24.8 35.5 22.7PG₈₃BP_(22.7)PPA_(24.8)MEEA_(35.5) IS-4 179 56.7 73.2 49.0PG₁₇₉BP₄₉PPA_(56.7)MEEA_(73.2)

The synthesis is exemplified for the polymer,PG₁₇BP_(4.3)PPA_(4.6)MEEA_(8.1): 2.05 g (1.69 mmol) of PG₁₇ (M_(n)=1214g/mol⁻¹, M_(w)/M_(n)=1.6), 2.21 g (8.57 mmol) of p-benzophenoxyaceticacid (BP), 1.35 g (8.57 mmol) of 1-piperidinepropionic acid (PPA), 1.77ml (11.4 mmol) of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA) and2.18 g (11.4 mmol) of p-toluenesulfonic acid monohydrate were added intoa 100 ml one-neck flask equipped with Dean-Stark and condenser. Then 40ml of toluene was added. The mixture was heated to 136° C. for 2 h,while water was removed azeotropically. Then 0.88 ml (5.7 mmol) of extraMEEA was added. The mixture was further reluxed for additional 4 h.After removing the solvent under reduced pressure, the residue wasdissolved in chloroform. The mixture was washed twice with 10% of NaOHaq and several times with NaCl aq until pH=7. After removing the solventunder reduced pressure, the residual water was removed by azeotropicaldestillation with toluene. The solution was filtered and the toluene wasremoved under reduced pressure. The residue was further dried at 40° C.in vacuum.

¹H NMR (CDCl₃): d=0.77, 1.32 (TMP core of PG); 1.14-1.64 (β and γ CH₂ inpiperidine ring); 1.98 (CH₃COO—); 2.13-2.66 (α CH₂ in piperidine ring,—NCH₂CH₂COO—); 2.98-5.42 (protons of PG and MEEA moieties, —OCH₂COO—);6.62-8.05 (protons of aromatic ring of BP moieties).

The synthesized photoreactive polymers displayed properties as disclosedby Table 11. TABLE 11 Photoreactive polymer M_(n) Yield IS-1 4176 86%IS-2 7929 53% IS-3 20500 58% IS-4 44400 53%

Example 2

This example illustrates the effectiveness of the photoreactive polymersin radiation curable compositions.

The curing efficiency of the photoreactive polymers was compared withthe combination of a low molecular weight synergist and photoinitiator.The molar ratio of the synergist and photoinitiator was kept constantfor both polymers and the low molecular weight comparison. The initiatorhad the same UV-VIS absorption spectrum as the photoreactive polymers.

The comparative radiation curable composition COMP-1 and the inventiveradiation curable compositions INV-1 and INV-2 were prepared accordingto Table 12. The weight % (wt %) was based on the total weight of theradiation curable composition. TABLE 12 wt % ot COMP-1 INV-1 INV-2DPGDATM 52.5 42.0 42.0 Sartomer ™ SR351 40.0 40.0 40.0 Initiator ILM-1 5.0 — — Co-initiator CLM-1  2.5 — — IS-1 — 18.0 — IS-2 — — 18.0Initiator ILM-1

Co-initiator CLM-1

The comparative radiation curable composition and the inventiveradiation curable compositions INV-1 and INV-2 were coated on anunsubbed 100 μ m PET substrate using a bar coater and a 10 μ m wiredbar. Each coated layer was cured using a Fusion DRSE-120 conveyer,equipped with a Fusion VPS/I600 lamp (D-bulb), which transported thesamples under the UV-lamp on a conveyer belt at a speed of 20 m/min. Thecuring speed was determined for the comparative radiation curablecomposition COMP-1 and the inventive radiation curable compositionsINV-1 and INV-2. The results are summarized in Table 13. TABLE 13Radiation curable Sensitivity composition % of maximum output COMP-1 160INV-1 130 INV-2 95

Table 13 shows that the inventive radiation curable compositions INV-1and INV-2 have a higher curing speed compared to the comparativeradiation curable composition COMP-1 with a state of the art commercialinitiator and co-initiator of low molecular weight. A percentage of morethan 100% of the maximum output of the lamp means that the speed of theconveyer belt had to be reduced to get the sample fully cured at themaximum output of the lamp. The higher the percentage, the more the belthad to be slowed down. A sensitivity of 160% means a belt speed of 12.5m/s at the maximum output of the lamp.

Example 3

This example illustrates the synthesis of a hyperbranched polyglycidolcore derivatized with benzophenone and 4-dimethylaminobenzoic acid.

The photoreactive polymers IS-5 and IS-6 were prepared and can berepresented by generalized formula IS-B.

Generalized Formula IS-B

wherein,

-   PG represents a hyperbranched polyglycidol core-   x represents the average number of terminal hydroxyl groups in the    starting polyglycidol

The hyperbranched polyglycidols selected for this example had differentmolecular weights:

-   PG₁₇: a hyperbranched polyglycidol with 17 hydroxyl groups on    average; and-   PG₃₃: a hyperbranched polyglycidol with 33 hydroxyl groups on    average.

The synthesis of IS-5 and IS-6 can be represented by the followingreaction scheme:

The photoreactive polymers IS-5 and IS-6 were prepared according toTable 14, which mentions the ratio of the different groups acylated ontoeach starting polyglycidol. TABLE 14 Photo- reactive polymer x DMBA MEEABP General formula IS-5 17 4.8 7.4 4.8 PG₁₇BP_(4.8)DMBA_(4.8)MEEA_(7.4)IS-6 33 9.3 12.3 11.4 PG₃₃BP_(11.4)DMBA_(9.3)MEEA_(12.3)

The synthesis is exemplified for the polymerPG₁₇BP_(4.8)DB_(4.8)MEEA_(7.4): A solution of 1.67 g (10.0 mmol) of4-dimethylaminobenzoic acid (DMBA) and 1.63 (10.0 mmol) of1,1′-carbonyldiimidazole (CDI) in 20 ml of THF was refluxed for 3 h.Then it was added to the flask containing 1.44 g (1.19 mmol) of PG₁₇ andthe mixture was refluxed overnight while stirring. A solution of 2.07 g(8.0 mmol) of p-benzophenoxyacetic acid, 1.23 ml (8.0 mmol) of MEEA and2.61 g (16.0 mmol) of CDI in 20 ml of THF was stirred at roomtemperature for 1 h, and then added to the cooled solution of DBpartially modified PG. The mixture was stirred at room temperatureovernight. Water was added to destroy the residual CDI and CDI activatedacids. After removing the solvent under reduced pressure, the residuewas dissolved in chloroform. The mixture was washed twice with 2N of HClaq, three times with deionized water, twice with 10% of NaOH aq andseveral times with NaCl aq until pH=7. After removing the solvent underreduced pressure, residual water was removed by azeotropicaldestillation with toluene. After filtration, the toluene was removedunder reduced pressure and the residue was kept at 40° C. in vacuumovernight.

¹H NMR (CDCl₃): d=0.77, 1.32 (TMP core of PG); 1.14-1.64 (β and γ CH₂ inpiperidine ring); 1.98 (CH₃COO—); 2.13-2.66 (α CH₂ in piperidine ring,—NCH₂CH₂COO—); 2.98-5.42 (protons of PG and MEEA moieties, —OCH₂COO—);6.62-8.05 (protons of aromatic ring of BP moieties).

Example 4

In this example compares the curing efficiency of the photoreactivepolymers IS-5 and IS-6 in a radiation curable composition with acombination of a low molecular weight synergist and photoinitiator. Themolar ratio of the synergist and photoinitiator was kept constant forboth polymers and the low molecular weight comparison. The initiator hadthe same UV-VIS absorption spectrum as the photoreactive polymers.

The comparative radiation curable compositions COMP-2 and COMP-3 and theinventive radiation curable compositions INV-3 and INV-4 were preparedaccording to Table 15. The weight % (w %) was based on the total weightof the radiation curable composition. TABLE 15 w % of: COMP-2 COMP-3INV-3 INV-4 DPGDA ™ 47.0 45.5 40.0 40.0 Sartomer ™ SR351 40.0 40.0 40.040.0 Quantacure ™ EHA 5.5 7.0 — — Initiator ILM-1 5.5 5.5 — — IS-5 — —18.0 — IS-6 — — — 18.0

The comparative radiation curable compositions COMP-2 and COMP-3 andinventive radiation curable compositions INV-3 and INV-4 were coated onan unsubbed 100 μ m PET substrate using a bar coater and a 10 μ m wiredbar. The coatings were covered with an unsubbed 100 μ m PET substrateand cured using a Fusion DRSE-120 conveyer, equipped with a FusionVPS/I600 lamp (D-bulb), which transported the samples under the UV-lampon a conveyer belt at a speed of 20 m/min. The curing speed was definedas the percentage of the maximum output of the lamp needed to cure thesamples. The results are summarized in Table 16. TABLE 16 Radiationcurable Sensitivity Viscosity composition % of maximum output (mPa · s)COMP-2 50 26.6 COMP-3 50 26.9 INV-3 50 55.5 INV-4 50 69.4

From Table 16 it can be concluded that the polymeric initiators were asefficient as their low molecular weight counterparts while the viscosityof the formulation stayed within the jettable region.

Example 5

This example illustrates the synthesis of a Boltorn™ H20 derivative asphotoreactive polymer for UV-curable compositions.

The photoreactive polymer IS-7 was prepared and can be represented bygeneralized formula IS-C.

Generalized Formula IS-C

wherein,

-   BH16 represents Boltorn™ H20 with a functionality of 16 and a Mw    (GPC) of 2100.

The synthesis of photoreactive polymer IS-7 can be represented by thefollowing reaction scheme:

4 g Boltorn™ H20, 2.08 ml (15 mmol) triethylamine and 0.46 9 (3.47 mmol)dimethylaminopyridine were dissolved in 40 ml THF. 2.74 g (15 mmol)4-dimethylaminobenzoyl chloride was added and the solution was refluxedfor 30 minutes. The mixture was allowed to cool down to roomtemperature. 3.79 g (15 mmol) 4-benzophenoxyacetic acid was dissolved in20 ml THF and 2.43 g (15 mmol) CDI was added and the reaction wasallowed to continue for 1 hour at room temperature. This solution wasadded to the Boltorn™ H20 solution and the mixture was refluxed for 6hours. The mixture was allowed to cool down to room temperature. 2.31 g(15 mmol) methoxyethoxyethoxyacetic acid was dissolved in 20 ml THF and2.43 g (15 mmol) CDI was added. The reaction was allowed to continue for1 hour at room temperature and this solution was added to the solutionof Boltorn™ H20. The reaction mixture was refluxed for 20 hours. 2 mlwater was added and the solvent was removed under reduced pressure. Theresidue was redissolved in 100 ml chloroform and extracted twice with 2N HCl, three times with water, twice with 10% NaOH and several timeswith brine until pH=7. The chloroform was dried over MgSO₄ and thesolvent was removed under reduced pressure. The residue was dried undervacuum at 40° C.

The photoreactive polymer IS-7 was prepared according to Table 17, whichmentions the ratio of the different groups acylated onto the Boltorn™H20 core. TABLE 17 Photoreactive polymer BP DB MEEA General formula IS-75.9 6.9 3.2 BH₁₆BP_(5.9)DB_(6.9)MEEA_(3.2)

The synthesized photoreactive polymer IS-7 displayed properties asdisclosed by Table 18. TABLE 18 Photoreactive polymer M_(n) Yield IS-74700 60%

Example 6

In this example the photoreactive polymer IS-7 was evaluated in aradiation curable composition.

The curing efficiency of the photoreactive polymer IS-7 was comparedwith a combination of a low molecular weight photoinitiator and a lowmolecular weight synergist. The molar ratio of the synergist andphotoinitiator was kept constant for both the polymer and the lowmolecular weight comparison. The initiator had the same UV-VISabsorption spectrum as the photoreactive polymers.

The comparative radiation curable composition COMP-4 and the inventiveradiation curable composition INV-5 were prepared according to Table 19.The weight % (wt %) was based on the total weight of the radiationcurable composition. TABLE 19 wt % of: COMP-4 INV-5 DPGDA ™ 43.0 40.0Sartomer ™ SR351 40.0 40.0 Initiator ILM-2 7.5 — Quantacure ™ EHA 7.5 —IS-7 — 18.0 Dibutyl phtalate 2.0 2.0

The comparative radiation curable composition COMP-4 and inventiveradiation curable composition INV-5 were coated on an unsubbed 100 μ mPET substrate using a bar coater and a 10 μ m wired bar. The coatingswere covered with an unsubbed 100 μ m PET substrate and cured using aFusion DRSE-120 conveyer, equipped with a Fusion VPS/I600 lamp (D-bulb),which transported the samples under the UV-lamp on a conveyer belt at aspeed of 20 m/min. The curing speed was defined as the percentage of themaximum output of the lamp needed to cure the samples. The results aresummarized in Table 20. TABLE 20 Radiation curable Sensitivity Viscositycomposition % of maximum output (mPa · s) COMP-4 50 25.3 INV-5 50 73.0

Table 20 shows that the photoreactive polymer IS-7 has a sensitivity,comparable with the low molecular weight reference and a viscositysuitable for ink-jet printing.

Example 7

This example illustrates the synthesis of a hyperbranched polyglycidolcore derivatized with carboxythioxanthone and 4-dimethylaminobenzoicacid.

The photoreactive polymer IS-8 was prepared according to Table 21 andcan be represented by generalized formula IS-D.

Generalized Formula IS-D

The synthesis of photoreactive polymer IS-8 can be represented by thefollowing reaction scheme:

1.67 g (10 mmol) 4-dimethylbenzoic acid was dissolved in 20 ml THF. 1.63g (10 mmol) CDI was added and the mixture was refluxed for 3 hours. 1.44g PG₃₃ was added and the mixture was refluxed over night while stirring.2.31 g (8 mmol) of the carboxythioxanthone and 1.23 ml (8 mmol)methoxyethoxyethoxyacetic acid were dissolved in 20 ml THF. 2.61 g (16mmol) CDI was added and the reactiion was allowed to continue for 1 hourat room temperature. This mixture was added to the PG₃₃ solution and thereaction was allowed to continue over night at room temperature. 2 mlwater was added and the solvent was removed under reduced pressure. Theresidue was redissolved in 50 ml chloroform and extracted twice with 2NHCl, three times with water, twice with 10% NaOH and several times withbrine until pH=7. The chloroform was dried over MgSO₄ and the solventwas removed under reduced pressure. The residue was dried under vacuumat 40° C. TABLE 21 Photoreactive polymer x TA DMBA MEEA General formulaIS-8 33 8.9 9.3 14.8 PG₃₃TA_(8.9)DB_(9.3)MEEA_(14.8)

The synthesized photoreactive polymer IS-8 displayed properties asdisclosed by Table 22. TABLE 22 Photoreactive polymer M_(n) Yield IS-88450 45%

Example 8

In this example the curing efficiency of the photoreactive polymer IS-8was evaluated in a radiation curable composition. The inventiveradiation curable composition INV-6 was prepared according to Table 23.The weight % (w %) was based on the total weight of the radiationcurable composition. TABLE 23 wt % of: INV-6 DPGDA ™ 40 Sartomer ™ SR35140 IS-8 18 Dibutyl phtalate 2

The inventive radiation curable composition INV-6 was coated on anunsubbed 100 μ m PET substrate using a bar coater and a 10 μ m wiredbar. The coating was covered with an unsubbed 100 μ m PET substrate andcured using a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/I600lamp (D-bulb), which transported the samples under the UV—lamp on aconveyer belt at a speed of 20 m/min. The curing speed was defined asthe percentage of the maximum output of the lamp needed to cure thesamples. The results are summarized in Table 24. TABLE 24 Radiationcurable Sensitivity Viscosity composition % of maximum output (mPa · s)INV-6 50 20.1

Table 24 shows that the photoreactive polymer IS-8 has a goodsensitivity, and a viscosity suitable for ink-jet printing.

Example 9

This example illustrates the synthesis of a hyperbranched polyglycidolcore derivatized with 2 different initiating functional groups and aco-initiating functional group.

The photoreactive polymers IS-9 to IS-12 were prepared according toTable 25 and can be represented by generalized formula IS-E.

Generalized Formula IS-E

TABLE 25 Photoreactive polymer x General formula IS-9 17PG₁₇TA_(2.1)BP_(2.2)PPA₅MEEA_(7.7) IS-10 33PG₃₃TA_(4.5)BP_(4.4)PPA_(8.9)MEEA_(15.2) IS-11 83PG₈₃TA₁₂BP₁₃PPA₂₆MEEA₃₂ IS-12 179 PG₁₇₉TA₂₇BP₂₁PPA₆₃MEEA₆₈

The synthesis is exemplified for PG₁₇TA_(2.1)BP_(2.2)PPA₅MEEA_(7.7). Amixture of 2.05 g PG₁₇, 1.1 g (4.29 mmol) 4-benzophenoxyacetic acid,1.35 g (8.57 mmol) 2-piperidinopropionic acid, 1.23 (4.29)2-thioxanthonoacetic acid and 2.18 g (11.4 mmol) p.-toluene sulfonicacid were dissolved in 40 ml toluene. The mixture was refluxed for 2hours, while water was removed azeotropically. After 2 hours, 2.65 ml(17.1 mmol) methoxyethoxyethoxyacetic acid was added and water wasremoved azeotropically for an additional 4 hours. The solvent wasremoved under reduced pressure and the residue was redissolved in 100 mlchloroform.

The mixture was extracted twice with 10% NaOH and several times withbrine until pH=7. The chloroform was dried over MgSO₄ and the solventwas removed under reduced pressure. The residue was dried under vacuumat 40° C. The other polymers were prepared according to a similarscheme. The yield and molecular weight is shown in Table 26. TABLE 26Photoreactive polymer M_(n) Yield IS-9 4230 86% IS-10 8400 45% IS-1121000 57% IS-12 45000 52%

Example 10

The curing efficiency of photoreactive polymers IS-9 and IS-10 wasevaluated in a radiation curable composition. The inventive radiationcurable formulations INV-7 and INV-8 were prepared according to Table27. The weight % (wt %) was based on the total weight of the radiationcurable composition. TABLE 27 wt % of: INV-7 INV-8 DPGDA ™ 40 40Sartomer ™ R351 40 40 IS-9 18 — IS-10 — 18 Dibutyl phtalate  2  2

The radiation curable compositions were coated on an unsubbed 100 μ mPET substrate using a bar coater and a 10 μ m wired bar. The coatingswere covered with an unsubbed 100 μ m PET substrate and cured using aFusion DRSE-120 conveyer, equipped with a Fusion VPS/I600 lamp (D-bulb),which transported the samples under the UV-lamp on a conveyer belt at aspeed of 20 m/min. The curing speed was defined as the percentage of themaximum output of the lamp needed to cure the samples. The results aresummarized in Table 28. TABLE 28 Radiation curable Sensitivity Viscositycomposition % of maximum output (mPa · s) INV-7 25 40.6 INV-8 50 37.8

Table 28 show that the inventive radiation curable compositions INV-7and INV-8 exhibit a good sensitivity and a viscosity suitable forink-jet printing.

Example 11

In this example, the influence of the molecular weight on viscosity fora hyperbranched photoreactive polymer is illustrated. The photoreactivepolymers IS-1 to IS-4 have been formulated into the inventive radiationcurable compositions INV-9 to INV-12 according to Table 29. TABLE 29 wt% of: INV-9 INV-10 INV-11 INV-12 DPGDA ™ 40 40 40 40 Sartomer ™ SR351 4040 40 40 IS-1 18 — — — IS-2 — 18 — — IS-3 — — 18 — IS-4 — — — 18 Dibutylphtalate  2  2  2  2

The inventive radiation curable compositions INV-9 to INV-12 were coatedon an unsubbed 100 μ m PET substrate using a bar coater and a 10 μ mwired bar. The coatings were covered with an unsubbed 100 μ m PETsubstrate and cured using a Fusion DRSE-120 conveyer, equipped with aFusion VPS/I600 lamp (D-bulb), which transported the samples under theUV-lamp on a conveyer belt at a speed of 20 m/min. The curing speed wasdefined as the percentage of the maximum output of the lamp needed tocure the samples. The results are summarized in Table 30. TABLE 30Radiation curable Sensitivity Viscosity composition % of maximum output(mPa · s) INV-9 50 53.4 INV-10 50 75.4 INV-11 50 54.4 INV-12 50 48.9

From Table 30 it is clear that even very high functional hyperbranchedphotoreactive polymers maintain their photoreactivity withoutinfluencing the formulation viscosity to a very high extend.

Example 12

This example illustrates that photoreactive polymers in a radiationcurable ink of the present invention are not likely to be extracted byfood when food packaging materials are printed upon.

The inventive radiation curable compositions INV-13 and INV-14 wereformulated according to Table 31. TABLE 31 wt % of INV-13 INV-14 DPGDA ™40 40 Sartomer ™ SR351 40 40 IS-5 18 — IS-6 — 18 Dibutyl phtalate  2  2

The radiation curable compositions INV-13 and INV-14 were coated on anunsubbed 100 μ m PET substrate using a bar coater and a 10 μ m wiredbar. The coatings were covered with an unsubbed 100 μ m PET substrateand cured using a Fusion DRSE-120 conveyer, equipped with a FusionVPS/600 lamp (D-bulb), which transported the samples under the UV-lampon a conveyer belt at a speed of 20 m/min. The full power of the lampwas used.

The cured sample (24×31 cm) and the PET overlay were extracted with THFby agitating the sample in a dipping tank filled with THF for 15minutes. The samples were rinsed with THF and the combined THF-solutionswere concentrated to 9 ml. The final volume of the THF-solutions wasadjusted to 10 ml. 100 μ l of this solution was filtered over a 0.45 μ mPVDF-filter and injected on a 3× mixed B column set and eluted withTHF/acetic acid 95/5. A refractive index detector was used. Theconcentration of extracted photoreactive polymers was estimated usingstandard solutions of the reference polymers.

The extracted amount of both IS-5 and IS-6 was lower than the detectionlimit of the analytics used to accurately determine the extractedamounts, which means that the extracted amount of residual IS-5 and IS-6is below 50 mg/m². This clearly illustrates that (almost) nophotoreactive polymer can be extracted from the cured layer, contrary tothe large amounts found for low molecular compounds, such as e.g.benzophenone.

Having described in detail preferred embodiments of the currentinvention, it will now be apparent to those skilled in the art thatnumerous modifications can be made therein without departing from thescope of the invention as defined in the following claims.

1. A radiation curable composition containing a photoreactive polymercomprising a dendritic polymer core with at least one initiatingfunctional group and at least one co-initiating functional group.
 2. Aradiation curable composition according to claim 1 wherein saidradiation curable composition is a radiation curable inkjet ink.
 3. Aradiation curable composition according to claim 2, wherein said atleast one co-initiating functional group is a co-initiating functionalgroup selected from the group consisting of an aliphatic amine, anaromatic amine and a thiol.
 4. A radiation curable composition accordingto claim 3, wherein said at least one initiating functional group isselected from the group consisting of benzophenones, thioxanthones,1,2-diketones and anthraquinones.
 5. A radiation curable compositionaccording to claim 4, wherein said dendritic polymer core is ahyperbranched polymer core.
 6. A radiation curable composition accordingto claim 2 wherein said at least one co-initiating functional group is aco-initiating functional group selected from the group consisting oftertiary amines, heterocyclic thiols and 4-dialkylamino-benzoic acid and4-dialkylamino-benzoic acid derivatives.
 7. A radiation curablecomposition according to claim 6, wherein said at least one initiatingfunctional group is selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.
 8. A radiation curablecomposition according to claim 7, wherein said dendritic polymer core isa hyperbranched polymer core.
 9. A radiation curable compositionaccording to claim 2, wherein said at least one initiating functionalgroup is selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.
 10. A radiation curablecomposition according to claim 9, wherein said dendritic polymer core isa hyperbranched polymer core.
 11. A radiation curable compositionaccording to claim 1, wherein said at least one co-initiating functionalgroup is a co-initiating functional group selected from the groupconsisting of an aliphatic amine, an aromatic amine and a thiol.
 12. Aradiation curable composition according to claim 11, wherein said atleast one initiating functional group is selected from the groupconsisting of benzophenones, thioxanthones, 1,2-diketones andanthraquinones.
 13. A radiation curable composition according to claim12, wherein said dendritic polymer core is a hyperbranched polymer core.14. A radiation curable composition according to claim 1 wherein said atleast one co-initiating functional group is a co-initiating functionalgroup selected from the group consisting of tertiary amines,heterocyclic thiols and 4-dialkylamino-benzoic acid and4-dialkylamino-benzoic acid derivatives.
 15. A radiation curablecomposition according to claim 14, wherein said at least one initiatingfunctional group is selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.
 16. A radiation curablecomposition according to claim 15, wherein said dendritic polymer coreis a hyperbranched polymer core.
 17. A radiation curable compositionaccording to claim 1, wherein said at least one initiating functionalgroup is selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.
 18. A radiation curablecomposition according to claim 17, wherein said dendritic polymer coreis a hyperbranched polymer core.
 19. A radiation curable compositionaccording to claim 1, wherein said photoreactive polymer has at leastthree initiating functional groups on the dendritic polymer core
 20. Aradiation curable composition according to claim 19, wherein saidphotoreactive polymer has at least three co-initiating functional groupson the dendritic polymer core.
 21. A radiation curable compositionaccording to claim 1, wherein said photoreactive polymer has at leastthree co-initiating functional groups on the dendritic polymer core 22.A radiation curable composition according to claim 1, wherein saiddendritic polymer core has at least one other functional group.
 23. Aradiation curable composition according to claim 22, wherein said atleast one other functional group is a compatibilizing group to improvethe compatibility of the photoreactive polymer with a radiation curablecomposition.
 24. A radiation curable composition according to claim 1,wherein said dendritic polymer core is a hyperbranched polymer core. 25.A radiation curable composition according to claim 24, wherein saidhyperbranched polymer core has a polydispersity M_(w)/M_(n) smaller than3.
 26. A radiation curable composition according to claim 24, whereinsaid hyperbranched polymer core is a polyglycidol.
 27. A process forpolymerization of monomers, oligomers and/or prepolymers comprising thesteps of: a) providing a photoreactive polymer, and b) admixing the saidphotoreactive polymer with monomers, oligomers and/or prepolymers,characterized in that said photoreactive polymer comprises a dendriticpolymer core with at least one initiating functional group and at leastone co-initiating functional group.
 28. A process for polymerization ofmonomers, oligomers and/or prepolymers according to claim 27, whereinsaid dendritic polymer core is a hyperbranched polymer core.
 29. Aprocess for polymerization of monomers, oligomers and/or prepolymersaccording to claim 28, wherein said hyperbranched polymer core has apolydispersity M_(w)/M_(n) smaller than
 3. 30. A process forpolymerization of monomers, oligomers and/or prepolymers according toclaim 29, wherein said hyperbranched polymer core is a polyglycidol.